In electrical junction boxes that are installed in automobiles and the like, a wiring board on which an electronic component, for example, is mounted, an insulation board equipped with a busbar, and the like are accommodated. As one kind of such electrical junction boxes, an electrical junction box is known in which an electronic control unit such as an ECU that accommodates a control circuit is used as a separate attachment body and is removably mounted to a mount portion of an electrical junction box main body. Since the electronic control unit is provided as a separate structure, such an electrical junction box has an advantage in that the electronic control unit can be easily replaced or changed, and so on.
In such electrical junction boxes, in order to improve the ease of operations for attaching and removing the attachment body to and from the mount portion of the electrical junction box main body, a configuration is employed in which the attachment body and the mount portion are rotatably assembled to each other via a removable hinge mechanism. Specifically, as disclosed in JP 2008-172889A, for example, a removable hinge mechanism constituted by a bearing and a shaft portion is provided on one end side of the mount portion and the attachment body, and in a state in which the shaft portion is inserted into and temporarily engaged with the bearing, the attachment body is rotated toward the mount portion. A lock mechanism constituted by a locking portion and a locked portion is provided on the other end side of the mount portion of the electrical junction box main body and the attachment body. Then, at a rotating end where opposing surfaces of the mount portion and the attachment body are placed one on top of the other, the attachment body is removably attached and fixed to the mount portion of the electrical junction box main body by means of the hinge mechanism provided on the one end side and the lock mechanism provided on the other end side. At this time, an electric circuit provided in the electrical junction box main body and an electric circuit provided in the attachment body are connected to each other by connecting connectors provided in the respective opposing surfaces.
However, in the hinge mechanism, which is provided on the one end side of the mount portion and the attachment body, a slight gap needs to be provided between the bearing and the shaft portion so as to allow rotation of the bearing and the shaft portion. Moreover, in the lock mechanism as well, which is provided on the other end side of the mount portion and the attachment body, a slight gap needs to be provided between the locking portion and the locked portion so as to allow the locked portion to pass over and engage with the locking portion as a result of elastic deformation and elastic return of the locking portion. Therefore, there is an inherent problem in that when vibrations from a vehicle body are transmitted when, for example, the vehicle is travelling, the attachment body vibrates relative to the electrical junction box main body due to the gaps in the hinge mechanism and the lock mechanism.
In addition, within a specific frequency range, resonance of the attachment body occurs and causes a significant increase in vibration acceleration applied to the attachment body as compared with vibration acceleration applied to the electrical junction box main body, and this results in the application of a large load on terminals of the connectors that connect the electrical junction box main body and the attachment body to each other. Consequently, breakage or the like of the terminals occurs, and thus there also is a risk that the stability of conduction between the electrical junction box main body and the attachment body is unable to be ensured.
Herein, the present invention was made in view of the above-described circumstances, and it is an object thereof to provide an electrical junction box including an attachment body that is assembled to an electrical junction box main body through a rotating operation, and having a novel structure that makes it possible to suppress vibration of the attachment body relative to the electrical junction box main body and advantageously ensure the stability of conduction between the electrical junction box main body and the attachment body.